Mapperly does not properly map DateTimeOffset to gRPC entities

[DaveNayMT]

Describe the bug
When mapping from a domain entity containing a DateTimeOffset property to a gRPC DTO containing a google.protobuf.Timestamp property, Mapperly does not set the correct property value. Instead the default value is assigned.

Declaration code

using Riok.Mapperly.Abstractions;

namespace Mapperly_gRPC.Services
{
    [Mapper]
    public static partial class ResponseMapper
    {
        public static partial HelloReply MapToHelloReply(this Response response);

        //private static Google.Protobuf.WellKnownTypes.Timestamp DateTimeOffsetToTimestamp(DateTimeOffset source)
        //{
        //    return Google.Protobuf.WellKnownTypes.Timestamp.FromDateTimeOffset(source);
        //}
    }
}

Actual generated code

// <auto-generated />
#nullable enable
namespace Mapperly_gRPC.Services
{
    public static partial class ResponseMapper
    {
        public static partial global::Mapperly_gRPC.HelloReply MapToHelloReply(this global::Mapperly_gRPC.Services.Response response)
        {
            var target = new global::Mapperly_gRPC.HelloReply();
            target.Message = response.Message;
            target.ResponseTime = MapToTimestamp(response.ResponseTime);
            return target;
        }

        private static global::Google.Protobuf.WellKnownTypes.Timestamp MapToTimestamp(global::System.DateTimeOffset source)
        {
            var target = new global::Google.Protobuf.WellKnownTypes.Timestamp();
            return target;
        }
    }
}

Expected generated code

// <auto-generated />
#nullable enable
namespace Mapperly_gRPC.Services
{
    public static partial class ResponseMapper
    {
        public static partial global::Mapperly_gRPC.HelloReply MapToHelloReply(this global::Mapperly_gRPC.Services.Response response)
        {
            var target = new global::Mapperly_gRPC.HelloReply();
            target.Message = response.Message;
            target.ResponseTime = MapToTimestamp(response.ResponseTime);
            return target;
        }

        private static global::Google.Protobuf.WellKnownTypes.Timestamp MapToTimestamp(global::System.DateTimeOffset source)
        {
            return Google.Protobuf.WellKnownTypes.Timestamp.FromDateTimeOffset(source);
        }
    }
}

Environment (please complete the following information):

• Mapperly Version: 3.3.0
• .NET Version: .Net 8
• Target Framework: .Net 8
• Compiler Version: 4.8.0-7.23572.1 (7b75981c)
• C# Language Version: 12.0
• IDE: Visual Studio v17.8.6
• OS: Windows 10

Additional context
Example project is available here: https://github.com/DaveNayMT/Mapperly_gRPC

[TimothyMakkison]

Hey, unfortunately this is "intentional" but not ideal. Mapperly will try to convert DateTimeOffset to Timestamp but was unable to find any matching properties or a valid constructor for TimeStamp that would accept DateTimeOffset as an value. It falls back to using the default parameterless constructor and never uses DateTimeOffset.

Expected Generated Code

Mapperly doesn't have ability to look for matching static constructors like Timestamp.FromDateTimeOffset. It could be possible but I suspect it isn't done in order to avoid weird behaviour.

As you've found, providing Mapperly with a DateTimeOffset -> Timestamp method fixes the issue. I understand this isn't perfect.

@latonz do you think it would be worth adding support for GRPC/Proto types? I suspect they are frequently used with Mapperly and would be appreciated by a lot of people.

[latonz]

I think adding support for non .NET types is not a good idea as this would get endless. Instead we could think about adding support for

• static methods on the target type named From{SourceType.Name} accepting the source type as a single parameter and the target type as return type
• static methods on the source type named To{TargetType.Name} accepting the source type as single parameter returning the target type

[latonz]

Closing this as it works as expected.